Inbred birds tend to get a raw deal in life. Bird populations with lower genetic diversity are less able to adapt to environmental change and stresses, and individuals that are inbred may have shorter wings, beaks that are less attractive to potential mates, or various other characteristics that make them less equipped to thrive in the wild. Some research has also found that inbred birds lead shorter lives. Now, a study suggests a shorter lifespan is actually written into their DNA—information that could be valuable for researchers and conservationists.

To conduct the research, published last week in Molecular Ecology, a team from the University of East Anglia (UEA) in Norfolk, England, homed in on a bird that had come extremely close to extinction: The Seychelles Warbler had dwindled to just 26 individuals in the '60s before its habitat was protected and it mounted a comeback. The researchers examined blood samples collected over 14 years from the population on Cousin Island near East Africa, focusing on pieces of DNA called telomeres.

Known to be a good predictor of lifespan, telomeres serve as protective caps on the ends of chromosomes, and they shorten with age and stress. The team found that inbred warblers had shorter telomeres than ones with greater genetic diversity. What’s more, telomeres were even shorter in warblers that had lived under the most stressful conditions, such as lack of food. (Because the environment on the island could be regularly monitored, the researchers knew exactly what pressures the birds experienced.) “Telomeres, they reflect everything—every stress you come across,” says lead author Kat Bebbington, a PhD student in UEA’s School of Biological Sciences.

This finding points to a perilous situation: Inbred birds are inherently set up for a shorter lifespan, but when they’re in a challenging environment, their lives are likely to be shortened even more. “That’s really important for conservation,” Bebbington says. “Often the reason that populations are small in the first place is because of things like deforestation and lack of food and habitat. If these populations are also inbred, that’s a recipe for trouble.”

The team could identify the telomere effect even when birds didn’t display more obvious signs of inbreeding. And that’s the real significance of the study, says Susan Haig, senior scientist and wildlife ecologist with the U.S. Geological Survey in Oregon. “If you go in and birds are flying around, how are you supposed to know that there’s a problem?” By looking at telomere length, researchers might now be able to quantify the extent of inbreeding. “It helps put a finer point on the exact status of a population,” Haig says.

Haig thinks the discovery could benefit conservation efforts for endangered species with disparate populations, particularly those that haven’t been studied extensively. “This tool could be useful for identifying which populations are suffering from inbreeding depression relative to the others,” she says. “It would help you to do a triage assessment of which populations are in need of most help immediately.”